The present invention describes new compounds. In particular it describes compounds for use in liquid crystal mixtures and in liquid crystal displays (LCDs) or in applications relating to inter alia thermography utilising nematic liquid crystal or chiral nematic liquid crystal mixtures.
LCDs, such as multiplexed Twisted Nematic TN-LCDs, Super Twisted Nematic STN-LCDs, Super Birefringent SBE-LCDs, Electrically Controlled Birefringence ECB-LCDs, or flexoelectric LCDs are currently used or being developed for computer monitors, laptop or notebook computers, portable telephones, video telephones, personal digital assistants, etc. The optical, electrical and temporal performance, e.g., contrast, threshold and driving voltages, and response times, of such displays depends crucially on the ratios of the elastic constants (k33, k22, k11) and the cell gap, d. In addition, flexoelectric LCDs also require nematic mixtures with advantageous ratios of the flexoelectric coefficients. Large banana shaped molecules have been found to increase the flexoelectric coefficients of nematic mixtures (1998, P57, Proceedings Freiburger Arbeitstagung Flxc3xcssigkristalle, Freiburg, Germany). However, due to their strongly non-linear shape and large number of aromatic rings and conjugated linking groups, they are highly viscous and relatively insoluble. They also exhibit high melting points and unusual smectic phases, which limits their miscibility with the nematic phase. Currently commercially available nematic mixtures for sophisticated high-information-content LCDs, such as STN-LCDs, incorporate trans-1,4-disubstituted-cyclohexyl derivatives with a terminal alkenyl chain (i.e., incorporating a carbon-carbon double bond) directly attached to the cyclohexane ring in order to produce the necessary elastic constant ratios for short response times, high multiplexing rates and low driving voltages. Such materials are costly and difficult to synthesise due to the requirement for a trans configuration of the 1,4-disubstituted cyclohexane ring and the necessity of synthesising the carbon-carbon double bond stepwise from this trans-1,4-disubstituted-cyclohexyl intermediate. If the carbon-carbon double bond is substituted at both carbon atoms, it must have a trans (E) configuration in order to exhibit an advantageous combination of elastic constants and to have an acceptably high nematic-isotropic transition temperature (N-I). The trans configuration is then generally produced by isomerisation of the cis (Z) form generated by the preceding Wittig reaction. These materials exhibit low or intermediate values of birefringence (xcex94n) due to the presence of the saturated cyclohexane rings. As the ratio d. xcex94n determines the optical properties of TN-LCDs and is fixed for driving the LCD in the first or second minimum, it is clear that higher values of xcex94n would allow smaller cell gaps. As the response time, ton of TN-LCDs is inversely proportional to d2, smaller cell gaps have a dramatic effect on ton. Low values of ton also allow the use of colour or more shades of colour due to the shorter frame times. Since the response times ton and especially toff also strongly depend on the magnitude of the viscosity of the nematic mixture, the combination of a low viscosity and a high birefringence would be highly advantageous. Furthermore TN-LCDs using thin film transistors (TFTs) as the backplate for active addressing require nematic liquid crystal mixtures with a positive dielectric anisotropy (xcex94xcex5) and a very high resistivity (holding ratio xe2x89xa798%) in order to avoid dielectric breakdown and inferior display performance. It has been shown that standard nematic liquid crystals with a terminal cyano group are unsuitable for TN-TFT-LCDs since they lead to low resistivity values due in part to their ability to solvate ions present in the alignment layers and electrodes. This has led to the wide-spread use of xe2x80x98super-fluorinatedxe2x80x99 nematic liquid crystals with terminal trifluoromethoxy (DE 3732284 A1), difluoromethyl (WO 90/01056) or fluorine endgroups (JP2-233626, EPA 0 568 040 A1, EPA 0 563 981 A2) and/or several lateral fluoro substituents. However, this leads in general to low nematic-isotropic transition temperatures (N-I) for two-ring compounds. This requires a disproportionate use of three-ring compounds resulting in a high viscosity for the nematic mixture. There is therefore a requirement for synthetically readily-accessible nematic liquid crystals of high birefringence, low viscosity advantageous ratios of elastic constants and flexoelectric coefficients, as well as a relatively high value of N-I and a low melting point.
Liquid crystals with a five-membered heterocyclic ring are known (DE 3346175; EP 0 461 620) and are reviewed in for example Wiss. Z. Univ. HalleXXIXxe2x80x280 M, H. 3, pp 35-55. They are generally characterised by a strong tendency for smectic phase formation (Mol. Cryst. Liq. Cryst., (1990), Vol.191, pp 223). Two-ring alkyl benzoates incorporating a five-membered heterocyclic ring, such as 2,5-disubstituted furan or 2,5-disubstituted 1,3,4-thiadiazole are known (EP 0 461 620; Mol. Cryst. Liq. Cryst., (1990), Vol. 191, pp 223). However, they are either non mesomorphic or exhibit smectic phases. Liquid crystals with a carbon-carbon double bond are also known (U.S. Pat. No. 4,676,604; U.S. Pat. No. 4,621,901; EPA 0195974; EPA 0315014; EPA 0355552) and are reviewed in for example Liq. Cryst., (1996) Vol. 20, pp 493. No alkenyl compounds incorporating a five-membered heterocyclic ring are described.
For all the above applications it is not usual for a single compound to exhibit all of the properties highlighted, normally mixtures of compounds are used which when mixed together induce the desired phases and required properties.
The present invention seeks to overcome or alleviate some of the above problems by incorporating a 5-membered heterocyclic ring in the core of a liquid crystal molecule in combination with a carbon-carbon double bond in the terminal end group of the molecule.
According to this invention compounds are provided of Formula I: 
wherein
RJ is CnH2n+1CHxe2x95x90CHCmH2mZ1 
n may be 1-5;
m may be 0-5;
q may be 0, 1 or 2;
A1, A2, are independently chosen from 2,5-disubstituted furan, 2,5-disubstituted thiophene, 2,5-disubstituted oxazole, 2,5-disubstituted thiazole, 2,5-disubstituted 1,3,4-oxadiazole, 2,5-disubstituted 1,3,4-thiadiazole, 1,4-disubstituted benzene, 2,5-disubstituted pyrimidine, 2,5-disubstituted pyridine, 2,6-disubstituted naphthalene;
laterally substituted 1,4-disubstituted benzene, laterally substituted 2,5-disubstituted pyrimidine, laterally substituted 2,5-disubstituted pyridine, laterally substituted 2,6-disubstituted naphthalene wherein the lateral substituents are independently selected from F, Cl, Br or CN and may be present in any of the available substitution positions;
A3 may be 2,5-disubstituted furan, 2,5-disubstituted thiophene, 2,5-disubstituted oxazole, 2,5-disubstituted thiazole, 2,5-disubstituted 1,3,4-oxadiazole, 2,5-disubstituted 1,3,4-thiadiazole, 1,4-disubstituted benzene, 2,5-disubstituted pyrimidine, 2,5-disubstituted pyridine, 2,6-disubstituted naphthalene; laterally substituted 1,4-disubstituted benzene, laterally substituted 2,5-disubstituted pyrimidine, laterally substituted 2,5-disubstituted pyridine, laterally substituted 2,6-disubstituted naphthalene wherein the lateral substituents are independently selected from F, Cl, Br or CN and may be present in any of the available substitution positions;
1,4-disubstituted bicyclo(2.2.2)octane, trans-1,4-disubstituted cyclohexane, trans-2,5-disubstituted dioxane, 1,4-disubstituted piperidine, Z1 may be O, COO, OOC;
Z2, Z3 are independently chosen from a direct bond, COO, OOC, C2H4, CH2O, OCH2, C4H8, C3H6O, (E)-CHxe2x95x90CHC2H4, (Z)-CH2CHxe2x95x90CHCH2, (E)-CHxe2x95x90CHCH2O, xe2x80x94Cxe2x89xa1Cxe2x80x94 R may be alkyl, alkoxy, alkenyl, alkenyloxy, alkanoyloxy, alkenoyloxy or OCpF2p+1, R may contain 1 to 20 carbon atoms and may be branched or a straight chain;
p is 1-20;
provided that:
when Z1 is O and m is 1, 3 or 5 the carbon-carbon double bond configuration in RJ is E and when
Z1 is O and m is 2 or 4 the carbon-carbon double bond configuration in RJ is Z and when
Z1 is COO or OOC and m is 0, 2 or 4 the carbon-carbon double bond configuration in RJ is E and when
Z1 is COO or OOC and m is 1, 3 or 5 the carbon-carbon double bond configuration in RJ is Z.
The structural and other preferences are expressed below on the basis of inter alia desirable liquid crystalline characteristics, in particular an advantageous combination of dielectric constants and high resistivity in the nematic phase, a high nematic-isotropic liquid transition temperature and ready synthesis from commercially available starting materials, some of which may already incorporate at least one carbon-carbon double bond with the desired configuration and position.
Preferably n is 1-3;
Preferably m is 0-3;
Preferably n+m is xe2x89xa66;
Preferably p is 3-7;
Preferably q is 0 or 1 and when q is 0 then both A1 and A3 are aromatic;
Preferably A1 is a five-membered heterocyclic ring;
Preferably A2 is 1,4-disubstituted benzene;
Preferably Z1 is O or COO;
Preferably Z2 and Z3 are direct bonds.
Overall preferred structures for formula I are those listed below: 
Preferably q is 0 or 1 and when q is 0 then A3 is aromatic;
Preferably A1, A2, are 2,5-disubstituted furan, 2,5-disubstituted thiophene, 2,5-disubstituted; oxazole, 2,5-disubstituted thiazole, 2,5-disubstituted 1,3,4-oxadiazole, 2,5-disubstituted; 1,3,4-thiadiazole, 1,4-disubstituted benzene;
Preferably Z1 is O, COO;
Preferably Z2, Z3 are direct bonds or xe2x80x94Cxe2x89xa1Cxe2x80x94
Preferably R is alkyl, alkoxy, alkenyl or alkenyloxy and has one to seven carbon atoms.
Especially preferred structures for formula I are those listed below: 
wherein R is alkyl, alkoxy, alkenyl or alkenyloxy and contains 1-7 carbon atoms.
According to a further aspect of this invention a liquid crystal mixture comprises at least one of the compounds of Formula I.
According to a further aspect of this invention a device comprises two spaced walls each bearing electrode structures and treated on at least one facing surface with an alignment layer, a layer of a liquid crystal material enclosed between the cell walls, characterised in that it comprises a compound of Formula I.
The device includes both passive and active devices and may be Twisted Nematic (TN) or a Super Twisted Nematic (STN) Device.
According to a further aspect of this inventiona bistable nematic liquid crystal device comprises;
two cell walls enclosing a layer of liquid crystal material;
electrode structures on both walls;
a surface alignment on the facing surfaces of both cell walls providing alignment to liquid crystal molecules;
means for distinguishing between switched states of the liquid crystal material;
a surface alignment grating on at least one cell wall that permits the liquid crystal molecules to adopt two different pretilt angles in the same azimuthal plane;
the arrangement being such that two stable liquid crystal molecular configurations can exist after suitable electrical signals have been applied to the electrodes;
wherein the layer of liquid crystal material comprises a material of Formula I.
The grating may have a symmetric or an asymmetric groove profile.
The grating may have an asymmetric groove profile which will induce a pretilt of less than 90xc2x0, e.g. 50xc2x0 to 90xc2x0. An asymmetric profile may be defined as a surface for which there does not exist a value of h such that;
xcexa8x(hxe2x88x92x)=xcexa8x(h+x)xe2x80x83xe2x80x83(1)
for all values of x, where xcexa8 is the function describing the surface.
The gratings may be applied to both cell walls and may be the same or different shape on each wall. Furthermore the grating profile may vary within each pixel area, and or in the inter pixel gaps between electrodes. One or both cell walls may be coated with a surfactant such as lethecin.
The liquid crystal material may be non twisted in one or both stable molecular configurations.
The cell walls may be formed of a relatively thick non flexible material such as a glass, or one or both cells walls may be formed of a flexible material such as a thin layer of glass or a flexible plastic material e.g. polyolefin or polypropylene. A plastic cell wall may be embossed on its inner surface to provide a grating. Additionally, the embossing may provide small pillars (e.g. of 1-3 xcexcm height and 5-50 xcexcm or more width) for assisting in correct spacing apart of the cell walls and also for a barrier to liquid crystal material flow when the cell is flexed. Alternatively the pillars may be formed by the material of the alignment layers.
The grating may be a profiled layer of a photopolymer formed by a photolithographic process e.g. M C Hutley, Diffraction Gratings (Academic Press, London 1982) p 95-125; and F Horn, Physics World, 33 (March 1993). Alternatively, the bigrating may be formed by embossing; M T Gale, J Kane and K Knop, J App. Photo Eng, 4, 2, 41 (1978), or ruling; E G Loewen and R S Wiley, Proc SPIE, 88 (1987), or by transfer from a carrier layer.
The electrodes may be formed as a series of row and column electrodes and an x,y matrix of addressable elements or display pixels. Typically the electrodes are 200 xcexcm wide spaced 20 xcexcm apart.
Alternatively, the electrodes may be arranged in other display formats e.g. r-xcex8 matrix or 7 or 8 bar displays.
The materials of the present invention may also be used in devices which make use of in-plane switching and this means that there may be electrodes on one or two of the substrates
Compounds of formula I can be prepared by various routes. Typically the aromatic heterocyclics can be prepared by the Suzuki aryl-aryl cross-coupling reaction (Chem. Rev., (1995) Vol. 95, pp 2457) of a aromatic boronic acid with an aromatic halide in the presence of a base such as aqueous sodium carbonate solution, a catalyst, such as tetrakis(triphenylphosphine)palladium(0), and a suitable solvent, such as tetrahydrofuran or 1,2-dimethoxyethane. Alternatively they can be synthesised by the Stille coupling of aryl stannanes with aryl halides in the presence of a catalyst, such as tetrakis(triphenylphosphine)palladium(0), and a suitable solvent, such as N,N-dimethylformamide or 1,2-dimethoxyethane (Angew. Chem., (1986) Vol. 98, pp 504). An alternative approach is the use of ring closure reactions. For example 2,5-disubstituted furan and 2,5-disubstituted thiophene derivatives can be prepared by treatment of a 1,4-disubstituted butanedione with phosphorous oxychloride or phosphorous pentasulphide, respectively, in a suitable solvent, such as pyridine (Z. Chem., (1975) Vol. 15, pp 222). 2,5-Disubstituted oxazole and 2,5-disubstituted thiazole derivatives can be prepared by treatment of suitable N-benzoyl-xcfx89-amino-acetophenone derivatives, formed in a one-pot-reaction from the corresponding 4-alkoxy-xcfx89-amino-acetophenone-hydrochlorides and 4-substituted-benzoylchlorides, with phosphorous oxychloride or phosphorous pentasulphide, respectively, in a suitable solvent, such pyridine (J. prakt. Chem., (1979) Vol. 321, pp 643). 2,5-Disubstituted-1,3,4-oxadiazole and 2,5-disubstituted-1,3,4-thiadiazole derivatives can be prepared by treatment of a bishydrazide derivative with phosphorous oxychloride or phosphorous pentasulphide, respectively, in a suitable solvent, such as pyridine (J. Amer. Chem. Soc., (1955) Vol. 77, pp 1850; J. prakt. Chem., (1980) Vol. 322, pp 933). Typically the ethers can be prepared by the Mitsunobu reaction (Synthesis, (1981) pp 1) of a phenol with an alcohol or alkenol in the presence of triphenyl phosphine, a dehydrating agent, such as diethyl azodicarboxylate, and a suitable solvent, such as tetrahydrofuran or N,Nxe2x80x2-dimethyiformamide. Alternatively they can be synthesised by alkylation of a secondary alcohol with alkyl or alkenyl bromide or the tosylate of the appropriate alcohol or alkenol in the presence of a suitable base, such as potassium tert.-butoxide, and a suitable solvent, such as tert.-butyl-methyl ether or 1,2-dimethoxyethane (J. Mater. Chem., (1994) Vol. 4, pp 1673). Alternatively they can be synthesised by alkylation of a phenol with an alkyl or alkenyl bromide or the tosylate of the appropriate alcohol or alkenol in the presence of a suitable base, such as potassium carbonate, and a suitable solvent, such as ethyl methyl ketone or cyclohexanone in a Williamson ether synthesis. 1,2-Disubstituted acetylenes and tolanes can be prepared by metal catalysed cross-coupling reactions of mono-substituted acetylenes with aryl and cyclohexyl halides or triflates in the presence of an appropriate base such as triethylamine and appropriate metal based catalysts such as tetrakis(triphenylphosphine)palladium(0) and copper(I)iodide or palladium(II) acetate and triorthotoluylphosphine ligands (Mol. Cryst. Liq. Cryst., (1990) Vol. 148, pp 193; Mol. Cryst. Liq. Cryst., (1995) Vol. 260, pp 93). The esters can be prepared by esterification (Angewandte Chemie (1978) Vol. 90, pp 556) of the appropriate phenol or secondary alcohol with an alkanoic acid or alkenoic acid in the presence of 4-(dimethylamino)pyridine, a dehydrating agent, such as N,Nxe2x80x2-dicyclohexyicarbodiiimide, and a suitable solvent, such as dichloromethane or N,Nxe2x80x2-dimethylformamide. Alternatively they can be synthesised by esterification of the appropriate phenol or secondary alcohol with an alkanoic or alkenoic acid chloride (produced, for example, from the corresponding alkanoic or alkenoic acid by the action of thionyl chloride or oxalyl chloride) in the presence of a base, such as pyridine or tnethylamine, and a suitable solvent, such as toluene or dichloromethane.
The invention will now be described, by way of example only, with reference to the following examples and diagrams: